An easy fix is to just update .travis.yml with this version bump.
A more laborious fix would be to somehow cache the compiled binary so that we don't build it every time Travis CI starts. Impressively, though, it still only runs for 49 seconds at this point in time, so perhaps it isn't really critical at all. https://travis-ci.org/exercism/sml/builds/656188797#L185
A new (March 2019) version of Poly/ML is available:
https://github.com/polyml/polyml/releases
An easy fix is to just update .travis.yml with this version bump.
A more laborious fix would be to somehow cache the compiled binary so that we don't build it every time Travis CI starts. Impressively, though, it still only runs for 49 seconds at this point in time, so perhaps it isn't really critical at all. https://travis-ci.org/exercism/sml/builds/656188797#L185